1. Field of the Invention
This invention relates to pipeline construction and more particularly it concerns a novel method for permanently installing large diameter pipeline along a predetermined grade.
2. Description of the Prior Art
The present invention is particularly suited to the installation of large diameter, gravity flow pipelines such as outflows, sewer lines, etc., many of which must be located under water near a shore line. In the past these pipelines, which are made up of a series of interconnected lengths of pipe, have been installed by first trenching the path along which the pipeline is to be installed, installing a layer of granular support material, such as gravel, in the trench, grading the support material to the desired final grade of the pipeline, and thereafter positioning each length of pipe with one end adjacent the end of a previously installed length of pipe on the thus graded support material. This technique proved unsatisfactory because it was difficult to provide precise grading of the support material, especially where the pipeline was to be installed under water. According to an alternative technique, preformed saddles were installed and set to desired grade level to serve as temporary supports. The pipe lengths were then set on these temporary supports and were thus held in place until a permanent support bed was installed. This technique, however, proved to be unsatisfactory because the saddles were expensive to manufacture and install.
The prior art also shows various other pipeline support techniques. For example, U.S. Pat. No. 3,734,138 to B. T. Brown et al and U.S. Pat. No. 3,861,158 to J. W. Swain et al show the use of flexible bags filled with a hardenable material and positioned at different locations along a pipeline to provide vertical support. These techniques, however, only provide point support at spaced apart locations along a pipeline. They are designed for the purpose of supporting a pipeline while allowing it to flex, to a certain degree, either at or between the supports. Because of this, these prior art techniques cannot provide the continuous firm support which is needed in a large diameter gravity type pipeline system. In a gravity type pipeline it is important that the pipeline follow a gentle yet continuous slope from inlet to outflow so that the materials passing through it can flow in an unobstructed fashion to the end of the line. If the line should flex or move in a vertical direction at any point along its length, the gravity flow will be impaired. Thus, where a large diameter gravity type line is to be installed it is especially important that the line be supported continuously along its length so as to ensure that the large weight of the fluids passing through it do not allow it to flex in the vertical direction.